The present invention relates to ceramic porous bodies in general and "ceramic foam filters" in particular. A "ceramic foam filter" is a filter particularly useful in the filtering of molten metal, which is made by immersing a polyurethane foam pattern into a ceramic slurry, removing excess slurry from the polyurethane foam pattern, and firing the polyurethane foam pattern to burn away the organic matter and thereby create a porous, hard, self-sustaining ceramic article.
Ceramic foam filters have been known for at least about twenty years. They were described almost simultaneously in U.S. Pat. Nos. 3,090,094 (Schwartzwalder et al.), 3,097,930 (Holland), and 3,111,396 (Ball). Since then a number of companies have worked to develop ceramic foam filters for use in the filtering of aluminum, copper, and other metals having a melting point of less than 1200.degree. C. Companies doing work in this field have included Swiss Aluminium Limited of Switzerland (U.S. Pat. Nos. 3,893,917, 3,947,363, 3,962,081, 4,024,056, and 4,081,371) and the Bridgestone Tire Company Limited of Japan (U.S. Pat. Nos. 4,257,810 and 4,258,099). Heretofore, however, there has not been available a ceramic foam filter which is suitable for use with superalloys, i.e., metals having melting points in excess of 1200.degree. C. In fact, prior to the development of the present invention several attempts were made to use presently available ceramic foam filters with superalloys but these efforts were unsuccessful.